By Ron Cowen
The 160 extrasolar planets discovered over the past decade constitute an odd menagerie. They include giant, Jupiterlike bodies with temperatures hot enough to melt metal, planets in orbits nearly as elongated as the paths of comets, and at least one distant cousin of Earth. But the planet announced last week seems the most bizarre of all. It displays the heaviest core of any planet yet detected.
With an orbit whose radius is only one-tenth that of Mercury’s path around the sun, the planet has a searing surface temperature of 1,500 kelvins, and it whips around the sunlike star HD 149026 in just 2.88 days. It’s likely to provide crucial new understanding of how planets form, says codiscoverer Bun’ei Sato of the Okayama Astrophysical Observatory in Japan.